Hydraulically actuated system



p i 9 J. c. WOODHOUSE ET AL 2,316,497

. HYDRAULIGALLY ACTUATED SYSTEM Filed 001. 28, 1941 3 Sheets-Sheet 1 JJZfi/Z (I mod/muse Emmet/2E F bliwr T W ATTORNEY p 1943. J. c. WOODHOUSEET AL 2,316,497

HYDRAULICALLY ACTUATED SYSTEM Filed Oct. 28, 1941 3 Sheets-Sheet 2 lm 6.oodiwse Kzmef/zE [9r ATTORNEY April 3, 1943. .J. c. WOODH OUSE ET ALHYDRAULIGALLY ACTUATED SYSTEM 3 Sheets-Sheet 3 Filed Oct. 28, 1941INVENTORS ATTORNY Patented Apr. 13, 19 43 UNlTD s'r r'rsur 2,316,497 10:r F s E HYDRAULICALLY ACTUATED SYSTEM 1941, Serial lilo. 416,806 3Claims. (Cl. 188-452) Application October 28 This invention relates tohydraulically-actuated, force-transfer systems, andmore particularly to,methods and means for inhibiting water accutmulation therein.

Modern hydraulically-actuated systems, especially automotive hydraulicbraking systems, require absolute freedom from gassing and decompositionor. the fluid at the temperatures met in operating conditions. Varioushydraulic fluids are available which, when first employed in ahydraulically-actuated force-transfer system, have sumciently highboiling points so that no gassing or vaporization occurs, but afterconsiderable periods of use, gassing or vapor-lock takes place undersevere operating conditions with consequent improper functioning. 7

It has now been found that this gassing or vaporization is the result ofa certain amount ofl water which has accumulated in the hydraulic fluid,reducing its boiling point to a dangerously low figure. Further, thediscovery has been made that practically all of the water found in ahydraulic fluid during normal operation of the force-transfer system isabsorbed from atmospheric air breathed through the small vent on thehydraulic fluid reservoir of the master cylinder.

It is an object of this invention to inhibit the accumulation of waterin a hydraulically-actuated, force-transfer system. It is a furtherobject to provide methods and means of preventing a lowering of theboiling point of hydraulic brake fluids during normal service operation.A still further object is to exclude atmospheric water vapor from ahydraulic brake system. Another object is to inhibit air pulsationthrough the vent of the master cylinder reservoir during normalactuation of the system.

.These and other objects hereinafter apparent are accomplished by thisinvention, the particular features and advantages of which will be madeclear by reference to the accompanying drawings and ensuing description.

In accordance with this invention. the disadvantages ofprior operationare overcome and water accumulation in a hydraulically-actuated,force-transfer system is inhibited by passing atmospheric air over adrying agent before it enters the master cylinder fluid reservoir, or bysubstantially preventing the breathing of air through the fluidreservoir vent on actuation of the sysrem, and preferably by acombination of the above steps of drying entering air and preventing airbreathing or pulsation.

A container filled with a drying agent is used to dry the entering airand when employed according to this invention has been found to beextremely effective during an extended operating period, particularly inautomobiles. A check valve is used to prevent air breathing or pulsationthrough the reservoir vent during actuation of the system.

Although the present invention is applicable to'anyhydraulically-actuated, force-transfer system or mechanism, thisinvention is especially applicable to automotive hydraulic brakesystems,

which form a preferred group of hydraulicallyactuated; force-transfersystems. Accordingly,

the ensuing detailed description is applied thereto, without intendingto restrict its scope to the particular details described.

Referringnow to the drawings:

Figure 1 represents a conventional automotive hydraulic braking systemwith the drying container and check valve of the present invention inplace upon the fluid reservoir air vent.

Figure 2 represents in sectional form a conventional hydraulic brakemaster cylinder with a conventional vented flllercap in place.

Figure 3 represents a filler cap with a master cylinder type check valvein place in accordance with the present invention.

Figure 4 represents a conventional filler cap withta flapper type rubbercheck valve in place.

Figure 5 represents aconvgntional filler cap with a Bunsen type checkvalve in place.

Figure 6 represents a filler cap to which is connected the dryingcontainer of this invention.

Figure '7 represents the drying container of Figure 6 with a Bunsen typecheck valve combined therewith.

Figure 8 represents the drying container of Figure 6 with a mastercylinder type check valve combined therewith.

Figure 9 represents the drying container of Figure 6 with a rubberflapper-type check valve combined therewith.

In normal operation of the hydraulic brake system, the brake system isfilled with hydraulic fluid and, referring to Figure 2, the reservoir Iis at least partially filled with fluid. The cylinder barrel 2 isprovided with a check valve 3 and plunger 4. The reservoir l isconnected with the cylinder barrel 2 through openings 5 and thereservoir I is in turn vented to the atmosphere by vent holes 6. When abrake application is made and the foot pedal 24 of Figure 1 is actuated,a geyser of fluid jets from the cylinder barrel 2 through the opening 5in front of the primary rubber cup into the reservoir l. The fluid istherebyaerated by air in the reservoir I, and at the same time a slightair pressure is built up in the reservoir l causing air to leave thevent holes 6. Upon re lease of the brakes, the master cylinder checkvalve 3 tends to maintain a slight pressure upon the service conduit, 25in Figure 1. Some fluid is drawn into the master cylinder barrel 2 asthe cup passes holes 5 causing air to enter through the vent holes 6 toreplace that previously expelled. This air pulsation or breathingactionjust described has been found to be the principal cause of moisturecondensation and accumulation in a hydraulic brake system. Some airpassage through the vent, for which it is intended, also occurs as aresult of temperature changes and normal losses of fluid from thesystem, e. g. seepage around the cups.

Figures 3, 4, and show in detail three types of rubber check valvesinstalled in filler plugs. In Figure 3, a rubber cone '8 is closelyfitted in a perforated conical housing 9 being retained by a crimp III;a bafile II is provided to prevent mechanical losses of fluid from thereservoir, and the usual air vents I2 are provided. Referring now toFigure 2, when the rubber check valve assembly of Figure 3 is installedin place of the flller cap I of Figure 2, this rubber check valve, inoperation, temporarily prevents air from leaving the reservoir I, andthereby prevents air pulsation with application of the brakes. Thispulsating, or breathing, normally attendant upon brake application isthereby inhibited, and with it the influx of moisture-laden air intoreservoir I of Figure 2.

Figure 4 shows a conventional filler cap in which two discs of rubber I3 and I4, form a flapper type check valve, the annular disc I3 beingattached to the cylindrical disc I4 at one point as shown, so that aclosely-fitting continuous contact between the two rubber discs isformed. The operation oi this valve assembly which replaces flller cap 1of Fig. 2, is substantially the same as the master cylinder type checkvalve of Figure 3;

In Figure 5, illustrating a Bunsen type check valve, the ordinary vents(6 of Figure 2) are sealed and a metal tube" is fitted with a closed,-slotted rubber tube I6 and vented to the atmosphere through vent holesII. In operation, the Bunsen valve assembly of Figure 5 replaces theconventional filler cap 'I in Figure 2. By replacing the ordinary ventedfiller cap 'I with a, flller cap equipped with a master cylinder checkvalve as represented by Figure 3 or a flapper type rubber check valvesuch as represented by Figure 4, or a Bunsen type check valve asrepresented by Figure 5, the breathing action through the air vent issubstantially inhibited and with it, the unnecessary influx ofmoisture-laden fresh air. Any one of these check valves operatessuccessfully to permit a slight pressure to build up in the reservoir Iduringbrake application while permitting the air passage necessary tocompensate for temperature-induced volume changes and normal fluidlosses resulting from seepage around the cups.

Referring now to Figure 6, a conventional filler cap 1 without the usualvent holes, is attached by a tubular conduit I8 to a container I 9. Acap II on the container I9 is provided with vents 2| to permit ingressand egress of atmospheric air. The containe is is fllled with a dryingagent 22 ing system, during the breathing action above described.

Figure '7 shows a Bunsen type check valve such as previously describedin connection with Figure 5, in place on the drying agent container I9of Figure 6, whereby the air is dried as it enters the reservoir and itsegress is retarded. Figures 8 and 9 show respectively a master cylindertype check valve such as described in connection with Figure 3 in placeupon the drying container IQ of Figure 6, and a'flapper type check valvesuch as described in connection with Figure 4 in place upon the dryingcontainer I9 of Figure 6. Both of these valves function similarly to theBunsen type check valve of Figure 7 to retard the escape of air, thuspreventing the breathing of air through the master cylinder vent duringbrake applications while at the same time permittin g normalcompensation for changes in air temper: ature and fluid volume in thereservoir I. r

The following examples illustrate the practice of the invention but itis not restricted theretoz Example 1.-Referring to Figure 6, a metaltube I9 about one inch in diameter and 8 inches long is closed at oneend except for a inch diameter hole into which a small copper tube I 8is soldered. The 8" x .1" tube I 9 is fllled with approximately 75 cc.of freshly activated alumina 22 held between two small plugs of cotton23, and the large opening of the tube is closed by means of a metal cap20 containing two /54" breather holes 2| The breaker holes in the mastercylinder fille cap. 'I are soldered shut and a copper pipe I8 issoldered into the filler cap. This latter pipe is coupled to the similarpipe on the tubular drying container I 8 in such a manner that any airdrawn into the master cylinder reservoir I of Figure 2 must pass overthe alumina 22 and be dried when the drying container assembly issubstituted for flller cap I of Figure 2.

The brake fluid used was made by reacting 35 parts by volume of castoroil with 15 parts by volume 01' fi-(methoxymethoxy) ethanol in the whichmay be silica gel, alumina gel, calcium sulfate, activated alumina,calcium chloride, adsorptive' carbon or other drying agent. Plugs 23,which may be of cotton or glass wool, finely perforated plates, porousplugs or similar material permitting transmission of gases and vapors,retain the drying agent in place. Referring to Figure 2, the assembly ofFigure 6 replaces the filler cap 'I of Figure 2, and it is apparent thatin nor mal braking operations all of the air entering the reservoir I ofFigure 2 must pass over and through the drying agent 22 of Figure 6.Water as vapor or liquid is inhibited from entering the brakcatalyst perliter.

presence of 42 grams of potassium ricinoleate The completeflind'contained 50 parts by volume of the above reaction mixture and 50parts by volume of fi-(methoxymethoxy) ethanol with incidental water inthe amount of 0.1-0.5%. The gassing temperature of this fluid is about340 F. which is higher than temperatures encountered under operatingconditions. The following results were obtained after several hundredthousand brake applications at temperatures up to F. and relativehumidities up to 55%:

, Water absorption0ontrcl i Brake Test No. applications Master G T WheelG T I cyl. cyl.

Per cent F. Per cent F. (1) 315,000 1.0 305 0.7 315 (2) 600,000 0.86 3090.76 313 Vt ater absorption-Irotectcd fluid Brake Test Nu. applicationsMaster G T Wheel G T cyl. cyl.

Per cent F. Per cent F. (1) 315,000 0.2 337 0.2 337 2) 000,000 0.13 3400.14 340 G. T is the gassing temperature 01' the fluid with the watercontent given. Test number 2 was conducted at an average atmospherichumidity lower than that of test number 1, and consequently thetotalwater absorption was lower than in test number 1.

600,000 strokes are equivalent to at least 60,000 miles of driving. Itis evident that the alumina drier 22 practically prevents any waterabsorption by the fluid in the brake system, since the amount found inthe protected system is about equivalent to the water introduced duringthe filling of the brake system.

Example 2.Referring to Figure 5, the usual breather holes in the mastercylinder flller cap I of Figure 2 are soldered shut, a /4" hole isdrilled through the top of the filler cap, and a x A," diameter metaltube I5 is soldered through the filler cap and allowed to extend abouton either side 01' the cap. The end of. the tube outside of the cylinderis closed off with solder, and two breather holes ll about /54" indiameter are drilled into the side of the tube. A slit about A" long ismade in a rubber tube 16 closed at one end and about /2 long, having adiameter that will makea tight connection when fitted over the end .ofthe metal tube l5 extending through the filler cap. The rubber tube isfitted to the metal tube I5, forming an ordinary Bunsen type valve andthe assembly is substituted for filler cap I of Figure 2. It operates bymaking it impossible to hold a vacuum on the system, but possible tohold a slight pressure on the system during brake application. Inoperation, no air is expelled from the reservoir l of the mastercylinder 2 upon the application of the brakes and, on the other hand,full compensation for changes in air temperature and fluid volume in thereservoir I is permitted. The following results were obtained with thisdevice operating with the same fluid as that in the preceding example attemperatures of about 90 F. and 45% relative humidity:

Similar results were obtained using an ordinary master cylinder checkvalve as illustrated in Figure 3 soldered in the filler cap in place ofthe Bunsen type valve above described. The valve was placed so thatpressure built up in the master cylinder forces the rubber valve lips 8against the metal valve body 9 tending to hold a slight pressure, whilea vacuum collapses the cup lip 8, and hence is released immediately.

Still another type of check valve which operates in the above manner isillustrated in Figure 4. It is composed of two rubber discs I3 and it,positioned in the filler plug or on the drying container previouslydescribed, through one of which there is a hole and the other isattached to and seats'against the first disc. Thus a check valve isformed, which tends to hold a slight pressure upon the reservoir I whilereleasing a vacuum;

Example 3.--Referring to Figure-7, the vent line on the drying containerused in Example'l is fitted with a Bunsen type valve as described inExample 2 and the assembly is fitted to the master cylinder reservoir.The Bunsen type valve reduces the passage of air over the drier to aminimum, thus prolonging the life of the drier and making it possible touse a smaller drying tube for the same period of use.

Although the foregoing description has shown tubular containers for thedrying agents, the invention is not limited thereto, since it is obviousthat many other containers for the drying agent will function equally aswell in the practice of the invention. The fluid reservoir itself, ifenlarged and provided with suitable retaining screens, may serve as thecontainer when the drying agent is silica gel or other substance inertto actual fluid contact.

In combining a drying tube with a check valve to prevent both moistureingress and breathing of air, the check valve may be positioned betweenthe atmosphere and the drying agent, or, ii deto permit a slight airpressure to build up in the reservoir while at the same time preventinga vacuum therein is well adapted for the purposes of this invention. Thecheck valve used must, of

course, be unable to hold such a pressure in the system that normalfunctioning of the brakes might be impaired. The check valve is designedmerely to prevent air pulsation through the breather holes and not topermit the retention of any substantial pressure permanently upon thefluid reservoir.

While the invention has been particularly described with reference topreventing the absorption of water by high boiling brake fluids, inorder that their boiling point he not reduced, it is neverthelessapplicable to any hydraulically actuated system to prevent accumulationof moisture therein. There are many other uses for bydraulic brake typeactuating systems such as to operate friction clutches, shittingmechanisms, traveling crane brakes, aircraft controls, and the like.Fluid couplings and fluid torque converters are also being used totransmit power on all types of moving vehicles. To insure satisfactoryoperation, the absorption of water by fluids used in such mechanismsshould be prevented. The methods and means described in this inventionare adaptable to prevent to a large extent the absorption of water byfluids used in such systems.

It is apparent that various changes may be made in the methods and meansdescribed with out departing from the spirit and scope of the inventionor sacrificing any of its advantages.

What is claimed is:

1. In a hydraulically-actuated system'including a plurality of slavecylinders, a master cylinder, a hydraulic fluid reservoir communicatinga with the master cylinder, air venting means for the hydraulic fluidreservoir and conduit means for transmitting hydraulic fluid pressurefrom the master cylinder to the slave cylinders, the

combination therewith of a container holding a 5 drying agent, thecontainer being in closed communication with the hydraulic fluidreservoir air venting means and being itself vented to the atmosphere ata point such that air entering the hydraulic fluid reservoir must firstpass over the 10 drying agent and be deprived of its water content.

2. The combination of claim 1 wherein the drying agent is selected fromthe group consisting oi activated alumina, silica gel, alumina gel, ac-15 tivated carbon, calcium sulfate and calcium chloride.

3. In a hydraulic bra lre system including a plurality 'of wheelcylinders, a master cylinder, a hydraulic fluid reservoir communicatingwith the master cylinder, air venting means for the fluid reservoir, andconduit means for transmitting fluid pressure from the master cylinderto the wheel cylinders, the combination therewith 01 means for retardingair escape from the hydraulic fluid reservoir and means for dryingatmospheric air entering the hydraulic fluid reservoir, the said meansfor retarding air escape being adapted to prevent air breathing orpulsation during brake application but not substantially to affectnormal compensation for volume changes. including temperatureandseepage-induced volume changes, within the system.

JOHN C. WOODHOUSE. KENNETH E. WALKER.

